CAD/CAM-based position/force control for a ball-end abrasive tool and its application to an industrial robot

Control of robotic mold polishing is considered in this paper. CAD/CAM-based position/force controller that simultaneously performs stable force control and exact pick feed control along curved surface is presented for industrial robots. The force feedback loop controls the polishing force consisting of the contact force and kinetic friction force. During mold polishing, the position feedback loop has a delicate contribution to the force feedback loop in Cartesian space so that the abrasive tool doesn't deviate from the desired trajectory and keeps a constant pick feed. When a mold polishing robot with the controller runs, cutter location (CL) data with normal vectors are used for not only a desired trajectory of tool translational motion but also desired contact directions given to a mold. The CL data allow the robot to realize a complete non-taught operation of the position and contact direction. In this paper, a simple experiment is conducted by using an industrial robot with a ball-end abrasive tool in order to evaluate the effectiveness of the proposed method. The target workpiece is an aluminum PET bottle blow mold after NC machining, whose curved surface has small cusp marks with about 0.3 mm height every pick feed. The results show that the proposed mold polishing robot with the CAD/CAM-based position/force controller can uniformly remove the cusp marks and further achieve mirror-like surface quality without undesirable over-polishing.